Mid-infrared interferometric monitoring of evolved stars

Karovicova, I.; Wittkowski, M.; Boboltz, D. A.; Fossat, E.; Ohnaka, K.; Scholz, M.

doi:10.1051/0004-6361/201116527

Cited by 20 publications

(38 citation statements)

References 56 publications

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“…3) do not show any significant variation from phase to phase and cycle to cycle. Finally, as reported by Karovicova et al (2011), no intra-cycle/cycle-to-cycle variations in visibility have been detected for the oxygen-rich Mira variable RR Aql which presents a visual lightcurve amplitude six magnitudes larger than the one of SV Psc. Therefore we can be confident that the difference in the visibility amplitude presented in Fig.…”

Section: N-band Spectrometric Variabilitymentioning

confidence: 79%

The geometry of the close environment of SV Piscium as probed by VLTI/MIDI

Klotz

Sacuto

Kerschbaum

et al. 2012

A&A

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Context. SV Psc is an asymptotic giant branch (AGB) star surrounded by an oxygen-rich dust envelope. The mm-CO line profile of the object's outflow shows a clear double-component structure. Because of the high angular resolution, mid-IR interferometry may give strong constraints on the origin of this composite profile. Aims. The aim of this work is to investigate the morphology of the environment around SV Psc using high-angular resolution interferometry observations in the mid-IR with the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI). Methods. Interferometric data in the N-band taken at different baseline lengths (ranging from 32-64 m) and position angles (73-142 • ) allow a study of the morphology of the circumstellar environment close to the star. The data are interpreted on the basis of 2-dimensional, chromatic geometrical models using the fitting software tool GEM-FIND developed for this purpose. Results. The results favor two scenarios: (i) the presence of a highly inclined, optically thin, dusty disk surrounding the central star; (ii) the presence of an unresolved binary companion at a separation of 13.7 +4.2 −4.8 AU and a position angle of 121.8 • +15.4 • −24.5 • NE. The derived orbital period of the binary is 38.1 +20.4 −22.6 yr. This detection is in good agreement with hydrodynamic simulations showing that a close companion could be responsible for the entrainment of the gas and dust into a circumbinary structure.

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Section: N-band Spectrometric Variabilitymentioning

confidence: 79%

The geometry of the close environment of SV Piscium as probed by VLTI/MIDI

Klotz

Sacuto

Kerschbaum

et al. 2012

A&A

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“…However, the detailed dust formation, condensation sequence, and massloss mechanisms are also not yet fully understood in the case of oxygen-rich AGB stars (cf., e.g., Karovicova et al 2013, for a recent discussion). Recent indications based on a polarimetric aperture masking technique (Norris et al 2012) and on mid-infrared interferometry (Wittkowski et al 2007;Karovicova et al 2011Karovicova et al , 2013 point toward transparent dust grains forming already at relatively small radii of about 1.5 stellar radii. These may be grains of amorphous Al 2 O 3 and/or magnesiumrich iron-free ("forsterite") silicates, while iron-rich silicates form at larger radii.…”

Section: Discussion On Alternative Mechanismsmentioning

confidence: 99%

What causes the large extensions of red supergiant atmospheres?

Arroyo-Torres

Wittkowski²,

Chiavassa

et al. 2015

A&A

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Aims. This research has two main goals. First, we present the atmospheric structure and the fundamental parameters of three red supergiants (RSGs), increasing the sample of RSGs observed by near-infrared spectro-interferometry. Additionally, we test possible mechanisms that may explain the large observed atmospheric extensions of RSGs. Methods. We carried out spectro-interferometric observations of the RSGs V602 Car, HD 95687, and HD 183589 in the near-infrared K-band (1.92−2.47 μm) with the VLTI/AMBER instrument at medium spectral resolution (R ∼ 1500). To categorize and comprehend the extended atmospheres, we compared our observational results to predictions by available hydrostatic PHOENIX, available 3D convection, and new 1D self-excited pulsation models of RSGs. Results. Our near-infrared flux spectra of V602 Car, HD 95687, and HD 183589 are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models, allowing us to determine the angular diameter and the fundamental parameters of our sources. Nonetheless, in the case of V602 Car and HD 95686, the PHOENIX model visibilities do not predict the large observed extensions of molecular layers, most remarkably in the CO bands. Likewise, the 3D convection models and the 1D pulsation models with typical parameters of RSGs lead to compact atmospheric structures as well, which are similar to the structure of the hydrostatic PHOENIX models. They can also not explain the observed decreases in the visibilities and thus the large atmospheric molecular extensions. The full sample of our RSGs indicates increasing observed atmospheric extensions with increasing luminosity and decreasing surface gravity, and no correlation with effective temperature or variability amplitude. Conclusions. The location of our RSG sources in the Hertzsprung-Russell diagram is confirmed to be consistent with the red limits of recent evolutionary tracks. The observed extensions of the atmospheric layers of our sample of RSGs are comparable to those of Mira stars. This phenomenon is not predicted by any of the considered model atmospheres including available 3D convection and new 1D pulsation models of RSGs. This confirms that neither convection nor pulsation alone can levitate the molecular atmospheres of RSGs. Our observed correlation of atmospheric extension with luminosity supports a scenario of radiative acceleration on Doppler-shifted molecular lines.

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“…Recent studies with VLTI/AMBER and VLTI/MIDI have provided information about the pulsation and the massloss of AGB stars (Ohnaka et al 2006Wittkowski et al 2007;Chiavassa et al 2010;Karovicova et al 2011Karovicova et al , 2013 and about the structure of the molecular distribution in AGB stars (Wittkowski et al 2008Martí-Vidal et al 2011). Quirrenbach et al (1993Quirrenbach et al ( , 2001) studied the TiO band (around 712 nm) in the atmosphere of cold giant stars (spectral type M).…”

Section: Introductionmentioning

confidence: 99%

VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters

Arroyo-Torres

Martí-Vidal

Marcaide

et al. 2014

A&A

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Aims. The main goal of this research is to determine the angular size and the atmospheric structures of cool giant stars ( Oct, β Peg, NU Pav, ψ Peg, and γ Hya) and to compare them with hydrostatic stellar model atmospheres, to estimate the fundamental parameters, and to obtain a better understanding of the circumstellar environment. Methods. We conducted spectro-interferometric observations of Oct, β Peg, NU Pav, and ψ Peg in the near-infrared K band (2.13−2.47 μm), and γ Hya (1.9−2.47 μm) with the VLTI/AMBER instrument at medium spectral resolution (∼1500). To obtain the fundamental parameters, we compared our data with hydrostatic atmosphere models (PHOENIX). Results. We estimated the Rosseland angular diameters of Oct, β Peg, NU Pav, ψ Peg, and γ Hya to be 11.66 ± 1.50 mas, 16.87 ± 1.00 mas, 13.03 ± 1.75 mas, 6.31 ± 0.35 mas, and 3.78 ± 0.65 mas, respectively. Together with distances and bolometric fluxes (obtained from the literature), we estimated radii, effective temperatures, and luminosities of our targets. In the β Peg visibility, we observed a molecular layer of CO with a size similar to that modeled with PHOENIX. However, there is an additional slope in absorption starting around 2.3 μm. This slope is possibly due to a shell of H 2 O that is not modeled with PHOENIX (the size of the layer increases to about 5% with respect to the near-continuum level). The visibility of ψ Peg shows a low increase in the CO bands, compatible with the modeling of the PHOENIX model. The visibility data of Oct, NU Pav, and γ Hya show no increase in molecular bands. Conclusions. The spectra and visibilities predicted by the PHOENIX atmospheres agree with the spectra and the visibilities observed in our stars (except for β Peg). This indicates that the opacity of the molecular bands is adequately included in the model, and the atmospheres of our targets have an extension similar to the modeled atmospheres. The atmosphere of β Peg is more extended than that predicted by the model. The role of pulsations, if relevant in other cases and unmodeled by PHOENIX, therefore seems negligible for the atmospheric structures of our sample. The targets are located close to the red limits of the evolutionary tracks of the STAREVOL model, corresponding to masses between 1 M and 3 M . The STAREVOL model fits the position of our stars in the HertzsprungRussell (HR) diagram better than the Ekström model does. STAREVOL includes thermohaline mixing, unlike the Ekström model, and complements the latter for intermediate-mass stars.

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Mid-infrared interferometric monitoring of evolved stars

Cited by 20 publications

References 56 publications

The geometry of the close environment of SV Piscium as probed by VLTI/MIDI

The geometry of the close environment of SV Piscium as probed by VLTI/MIDI

What causes the large extensions of red supergiant atmospheres?

VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters

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